week 1 & 2 inspection & testing (basic) (powerp point file)

7/30/2019 WEEK 1 & 2 Inspection & Testing (Basic) (powerp point file)

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1

A problem with many installations,

particularly domestic, is that

Every man and his dog has had a

hand in it


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2

periodic inspection and testing to ensure

continued safety is unlikely.

additions/alterations possibly undertaken

by unqualified persons.

The domestic electrical installation

likely to have been originally installed

by competent electrical contractor


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3

To what standards should anelectrical installation conform?

The Institution of ElectricalEngineers Wiring Regulations


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4

First Edition of the Regulations

Issued in 1882 and entitled

Rules and Regulations for thePrevention of Fire Risks

Arising from Electric Lighting


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What about risk of electric shock

and death by electrocution?


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Jointly owned by the Institution of

Electrical Engineers and B.S.I.

Latest edition

1st January 2002

Came into effect


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Are these regulations statutory?

No, but they can be used as

evidence of compliance withstatutory regulations

limited value within the domesticinstallation in terms of enforcement


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Very few enforceable regulations

apply to domestic installations


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The commercial or industrial electrical

installation usually under the controlof competent persons.

Statutory measures in place toensure a safe working environment.

This includes the electricalinstallation and electrical equipment


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Failure to comply with statutory regulations

within the workplace can lead to criminalprosecution


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Other Interested Parties


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Two organisations concerned with the

quality and safety of all aspects of electricalinstallation work in including domestic


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The Electrical Contractors AssociationE.C.A.

National Inspection Council for Electrical

Installation Contracting

N.I.C.E.I.C.


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Organisations only concerned with the

competence and quality of work for

those electrical contractors whoare members of their organisation


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What happens if an electrical contractor

carries out work in an unsatisfactory

manner?

If the contractors are members of the ECAor NICEIC, then appropriate action can be

taken

If not, the trading standards office, or local

authority may be able to help


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With many domestic installations there is

little or no maintenance undertaken toensure continued safety

In many cases, the integrity and safety ofthe installation is reduced by the D.I.Y.person!


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The need for Inspection and Test


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Installations should be inspected and tested

before being put into service -

(initial verification)

at regular intervals thereafter -

(periodic)

on completion of any alterations or

additions


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The Initial Verification


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For an initial verification

BS 7671:2001 states:

installed equipment to an appropriatestandard, i.e. BS, BS EN etc.

correctly selected and erected

not visibly damaged or defective as to

impair safety


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The periodic installation inspection

BS 7671:2001 states

Periodic inspection and testing of an

electrical installation shall be carried out todetermine,so far as is reasonably

practicable, whether the installation is in a

satisfactory condition for continued service


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Generally, the main reason for undertaking

an inspection and test is to ensure that theinstallation is safe to use


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What are the likely reasons for an

installation failing to be safe?

Age

Wear and tear - may be considerable inrented accommodation

Botched work by incompetent persons, or

unscrupulous contractors


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Periodic Inspection Report

Where is it required?

expiry of current certificate

change of ownership or use

as a result of damage - flood, fire, etc

mortgage/insurance purposes


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Factors affecting the safety

some common factors will include:-


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Damage to equipment or accessories

Poorly installed equipment/accessories

Loose connections giving rise to shock/fire

Overloaded circuits

Inadequate protection of circuits against

overcurrent

Circuit cables inadequate to safely carryload current

Inadequate earthing arrangements


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The visual Inspection


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For reasons of safety the supply

should preferably be switched offprior to conducting the inspection


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Checking fixings of accessories

and cabling


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Loose connections may result in

electric shock

fire


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circuit connections may be dislodged bymovement of the socket outlet .

terminations should be checked beforesocket is secured

remember, loose

connections may

give rise to fireand shock


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circuit connections may be dislodged bymovement of the joint-box .


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Thats assuming they bothered to usea joint box in the first place.


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Blimey hes even left

the screwdriver bit

in the terminal block

potential fire/shock risk due to mechanical

damage or loose connections


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Overheating due to loose connections


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Correct connection of single-way switch


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Correct connection of single-way switch

surface box secure

earth wire sleeved

terminations secure


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Basic one-way lighting circuit

switch

Lamp

P

N


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switch

lamp

P

N


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Switch connectionsfor two-way lighting


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P

N


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P

N


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P

N


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P

N


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P

N


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When converting one-way

to two-way lighting the earth

wire used as live conductor

Very dangerous practice


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When installing socket outlets


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Fuses and Circuit Breakers


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The purpose of a fuse or circuit breaker

device is automatically to interrupt circuit

current in the event of fault or overloadconditions

E i t fl lt f


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Excessive current may flow as a result of:

overload (excessive connected load)

short circuit between live and neutral

earth fault (live or neutral to earth)

Overload


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Overload

(excessive connected load)


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Under normal circumstances the fuse or

circuit breaker should operate before the

circuit cables reach a dangerously hightemperature


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If the fuse or circuit breaker is to high for

the circuit, the cables may reach a dangerouslyhigh temperature resulting in fire


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Short circuit


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Phase and neutral conductors touching

Phase to neutral short resulting fromloose connections at a socket outletLarge fault current flows - fuse or circuit

breaker should operate


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Combined main switch and r c d


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Least sensitive of the two devices and protectscircuits feeding fixed equipment.

Combined main switch and r.c.d.

Earth fault


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a fault condition that exists between liveconductors and earth

Excess current should cause fuse orcircuit breaker to operate


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rewirable fuse -

most widely abused


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Incorrect size of element

Most likely reason fordevice failing to operate


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fuse element too large


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a fuse failing to operate under

fault conditions may wellresult in fire


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The Rewirable fuse is an antiquated

device. even with the correct

rating of fuse element it may not safelyinterrupt high levels of fault current

Cartridge fuses to BS 1361


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Cartridge fuses to BS 1361

scattering of hot metal particles

contained within cartridge thusreducing fire risk duringoperation

operates much closer to itscurrent rating when compared tothe rewirable fuse


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has the ability to interrupt high levels of faultcurrent

less likelihood of premature failure due to

oxidisation when compared to the rewirable


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Selection of fuses used in consumer units


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Circuit-breakers to BS EN 60898


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Circuit breakers to BS EN 60898

most widely used type of

overcurrent protective device,particularly for domestic applications

Thermal-magnetic operation

thermal - overload

magnetic - short circuit conditions

Older miniature circuit breakers toBS 3871

Circuit-breakers to BS EN 60898


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rating (A) application

6 lighting circuits

20 13A socket radial

32 13A socket rings

32 13A socket radial

45 cooker/shower circuits

3 bell transformers

16 immersion heaters

The Residual Current Device (r.c.d.)


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The Residual Current Device (r.c.d.)

Provides protection against earth faults interms of:

electric shock, and

fire of an electric origin


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Why bother with an r.c.d. when a fuse or circuit

breaker can provide protection against earth fault

conditions?


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an r.c.d can operate in the region of milli-amps

in fact a r.c.d. rated at 30mA can provide

protection against electrocution


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fuses and circuit breakers require relatively

high currents in order to operate

for example, for a 30A rewirable fuse requiresapproximately 200A to operate within a safe

time period


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Types of r.c.d.

Socket outlet incorporating r.c.d. protection


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Socket outlet incorporating r.c.d. protection

High level of personal

protection against shock,

particularly when using

portable electricalequipment outdoors

Domestic consumer unit with two r.c.d.s


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Extensively used in conjunction with an earthelectrode earthing system

Providing personal protection


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Second r.c.d. has greater sensitivity and isused to protect socket outlet circuits

g p p

Combined r.c.d. circuit breaker (RCBO)


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single device providesprotection against both

overload, short circuit andearth fault currents

Combined r.c.d. circuit breaker (RCBO)


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An r.c.d. is a device which can provide protection

against:

fire resulting from earth faults

earth faults where circuit resistance is too highfor protection by conventional devices, i.e.circuit breakers or fuses

where greater protection against electric shock,for example socket outlet circuits likely tosupply portable equipment outdoors


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fuses and circuit breakers are totally unable to

provide this level of shock protection


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What rating of r c d are generally available and


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What rating of r.c.d. are generally available and

where would they be used?

as a guide


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30mA for personal protectionsocket outlet circuits

100mA or above for protection

against fire


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P

N

E


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Correct polarity


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Edison-screw

p y

Correct polarity of Edison-type screw

fittings essential if shock is to be avoided


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Centre contact must always be connected

to the phase conductor of the supply

P

N


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neutral

phase


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Phase

Neutral

Phase and neutral connections reversed

Reversed polarity


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A person removing an Edison-screw lamp

could receive a serious electric shock if

they touched the lamp thread before ithad completely been removed from the

fitting

Reversed polarity


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The socket tester


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useful but limited in its application


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All lights green indicates correct polarity


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red - red -green indicates P-E reversed


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The socket tester will INDICATE


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The socket tester will INDICATE

THE PRESENCE OF SUPPLY

IDNETIFY THE CORRECT POLARITY OF THEPHASE CONDUCTOR

THAT SOME FORM OF EARTH CONNECTION ISPRESENT AT THE SOCKET OUTLET

The socket tester will NOT INDICATE


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The socket tester will NOT INDICATE

A HIGH RESISTANCE EARTH PATH

A REVERSED NEUTRAL

EARTH CONNECTION

AND ABOVE ALL


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NEVER USE A SOCKET TESTER TO PROVETHAT A CIRCUIT IS ISOLATED, (dead).

AND ABOVE ALL

Earthing


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In order to prevent electric shock the exposedmetalwork of electrical appliances, metal

conduit etc should be earthed.

In the majority of cases the earthing facility is

provided by the local electricity supplier.


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Inadequate earthing arrangements may lead

to electric shock or death through electrocution


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Earthing arrangements

Typical domestic intake


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112main incoming earth

earth

terminal

consumer unitmeter

service cutout

Earth connection is obtained from supplierssheath (main incoming cable)


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sheath (main incoming cable)

This method of earthing is still widely usedand is reliable

Modern earthing arrangement where the earth

is connected to the incoming neutral at the


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is connected to the incoming neutral at theservice head

Rapidly becoming the most widely used

supply arrangement

Widely used in agricultural/rural areas.

Earthing relies on earth electrode (rod/spike)


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Gradually being phased out wherever possible

Earthing relies on earth electrode (rod/spike)

Earth rod and typical enclosure


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Earth rod and typical enclosure

Problems with earth electrodes


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generally does not provide a very good

earth return path

liable to corrosion and mechanical

damage

week 1 & 2 inspection & testing (basic) (powerp point file)

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